The spending included $13.1 million to support Republicans and another $16.5 million to oppose Democrats. At $6 million, the chamber’s top recipient was Sen. Pat Toomey, R-Penn., who retained his seat.

Public Citizen charged the spending “makes it clear that rather than being a voice for American business, the chamber has become an arm for the Republican Party.”

“Companies that are chamber members should ask themselves if such a partisan voice really represents their best interests,” said Lisa Gilbert, director of Public Citizen’s Congress Watch division.

The chamber, a trade association organized under section 501(c) of the tax code, is not legally required to disclose what it spends on elections, but the group analyzed campaign spending data from the Center for Responsive Politics.

A spokesman for the chamber said it had endorsed six House Democrats and that five of the six won.

“Our spending was very targeted and focused on key Senate races where there was a stark contrast between the candidates,” said Blair Latoff Holmes. “The chamber supports pro-business candidates who have the courage to govern.”